Essentially that's what happens for the ink catridge, they just put more ink in it. I have no idea how they would do that for a laser, I'd assume that either the drum roll will be replaced, I would be weary of this.Cartridge World USA | World Leader in Printer Cartridge Refilling (and how does it work with this operation - do you take your old cartridges to them and then have to come back later for the refilled??) I don't want to refill the current Laserjet toner cartridge since I think the thing is dodgy to begin with!
Printers will always tell you it's running out long before it's actually ready, I had this happen a day ago, the printer refused to print because it was "empty" and reset it and it printer fine.
Here's a line from a study about printers "That's the first problem. Printers routinely report that they are low on ink even when they aren't, and in some cases there are still hundreds of pages worth of ink left. "
[Source: Study: Inkjet printers are filthy, lying thieves]